A feed-through capacitor connects to a conductive shaft or stud that passes through a chassis wall, and it filters unwanted high-frequency electromagnetic interference from an electrical circuit. A feed-through capacitor may be used on either an input or output conductor, and it prevents electromagnetic interference from getting into or out of the circuit. Feed-through capacitors are generally positioned close to a connection interface in order to isolate the connection from electromagnetic interference.
Feed-through capacitors are connected from a conductor to the chassis of a device and they provide a path for high frequency current to flow from the conductor to the chassis. In a typical feed-through capacitor, a capacitive element surrounds the stud and is coupled to both the stud and the inside of the chassis wall. The capacitive element provides a low impedance path from the stud to the chassis wall. However, the capacitive element appears as an insulator to low frequency current, and therefore it does not divert the low frequencies from the stud to the chassis. High frequencies, in contrast, are shunted from the stud to the chassis. In essence, a feed-through capacitor is a short circuit that only short-circuits frequencies that are undesirable for a particular application. Feed-through capacitors generally operate in the kilohertz to megahertz range.
Feed-through capacitors are typically made for small contacts and small currents, and are commonly used in low power, radio frequency applications. In high power applications, and particularly high current applications, there is no generally accepted method for applying feed-through capacitors to a circuit. High power applications require capacitors with large capacitance. Most feed-through capacitors utilize ceramic discs as their dielectric layer and, since capacitance is proportional to the size of the capacitor's dielectric layer, high power applications require capacitors with large ceramic discs. Because ceramics are brittle by nature, it is difficult to make ceramic discs large enough for use in capacitors for high power circuits.
Therefore, there is a need in the art for a feed-through capacitor that is able to work effectively in high power, and particularly high current, circuits. It is also desirable that the feed-through capacitor be simple and inexpensive to manufacture, yet sturdy enough for industrial applications.